Under in vitro conditions, neuroscientists study neutral activities in brain tissue with single electrode intercellular and extra cellular recording techniques. By way of example, a portion of brain tissue is removed to preserve the features of interest. Once removed, the brain tissue is sliced by a microtone to produce a thin, predetermined slice of brain tissue. This resulting slice of brain tissue may be mounted on the glass slide for viewing with a microscope.
In order to analyze the brain tissue's reaction to chemical stimulation, the slice of brain tissue is often exposed to a bath of the chemical stimulus. Unfortunately, the chemical bath activates all relevant receptors in the slice of brain tissue. As such, it is difficult to ascertain the underlying cellular mechanisms that contribute to neural network reconfiguration, plasticity and behavior. Alternatively, a microinjection technique may be used wherein the chemical stimulus is localized to a specific region of the slice of brain tissue. However, as is known, microinjection techniques provide the neuroscientist with very little control over the timing and distribution of the chemical stimulus. Consequently, it is highly desirable to provide a method and apparatus that allows a neuroscientist to deliver a chemical agent to a specific region of a slice of tissue with high spatial and temporal resolution.
As is known, nerve cells, like all living cells, maintain an electrical charge across their outer membrane. By recording the electrical activity produced by the nerve cells in response to a predetermined stimulus, new discoveries in learning, memory, motor control, pain, principles of neuro network function and the like may occur. Since the electrical signals produced by nerve cells are relatively small, such electrical signals must be amplified before they can be measured accurately. In order to amplify these signals, one or more electrodes are placed adjacent the desired tissue and are operatively connected to an electronic amplifier. The size and the placement of the electrodes adjacent the brain tissue determines what aspects of neural activity will be recorded. It can be appreciated that large electrodes are utilized to record the activity of large populations of nerve cells, while small electrodes are utilized to record more localized neuroelectric events. However, as heretofore described, a high level of precision and control is necessary when interfacing with neurons, due to the dynamic timing scale of neurological events. Consequently, it is highly desirable to provide an electrode device that precisely records and/or stimulates a specific region of a slice of brain tissue for purposes of data collection and experimental control.
Therefore, it is a primary object and feature of the present invention to provide a method and apparatus capable of delivering precise amounts of chemical stimuli to neurons of a biological object with a high degree spatial and temporal resolution.
It is a further object and feature of the present invention to provide a method and apparatus for recording electrical activity from a large number of neurons in vitro while simultaneously delivering chemical stimuli to neuronal subpopulations with high spatial and temporal resolution.
It is a still further object and feature of the present invention to provide a method and apparatus for studying individual neurons in a slice of a biological object that is inexpensive and versatile.
In accordance with the present invention, a micro device is provided for examining and testing a slice of a biological object. The micro device includes a body defining a chamber therein and an electrode projecting in the chamber. The electrode has a first end for receiving the slice of the biological object thereon and a second end connectable to a monitoring device.
The body includes a base having an upper surface and a cover receivable on the upper surface of the base. The chamber extends into the base from the upper surface and terminates at a closed end. The first end of electrode lies in a plane generally co-planer with the upper surface of the base. The body also includes a flow channel in communication with the chamber and a first pulse channel communicating with the flow channel. The first pulse channel has a first input portion with an output communicating with the flow channel and a second output portion with an input communicating with the flow channel. A fluid stream flows through the flow channel and a pulse fluid flows between the output of the output portion of the first pulse channel and the input of the output portion first pulse channel.
The body may also include a second pulse channel communicating with the flow channel. The second pulse channel includes a first input portion having an output communicating with the flow channel and a second output portion having an input communicating with the flow channel. In such arrangement, the fluid stream flows through the flow channel and a first pulse fluid flows through the flow channel between the output of the output portion of the first pulse channel and the input of the output portion of the first pulse channel. The first pulse fluid has a variable cross sectional area. In addition, a second pulse fluid flows through the flow channel between the output of the output portion of the second pulse channel and the input of the output portion of the second pulse channel. The second pulse fluid also has a variable cross sectional area
Further, the body may include first and second input channels. The first and second input channels have outputs communicating with the flow channel. The output of the first input channel communicates with a first side of the flow channel and the output of the second input channel communicates with a second side of the flow channel.
In accordance with a further aspect of the present invention a micro device is provided for examining and testing a biological object. The micro device includes a body defining a chamber and a channel in communication with the chamber. A stimulation fluid flows axially along a flow path in the channel. The stimulation fluid engages a user selectable region of the biological object.
It is contemplated to provide a support structure in the chamber for supporting the biological object thereon. The support structure includes an array of electrodes projecting in the chamber. At least one of the electrodes has a first end for receiving the biological object thereon. The electrodes are connectable to a monitoring device for recording electrical activity and providing stimuli to the biological object.
The micro device may also include a flow control structure for altering the flow path of the stimulation fluid such that the stimulation fluid engages the user selected region of the biological object. The flow control structure includes first and second guide fluids flowing in streams along corresponding flow paths in the channel on opposite sides of the stimulation fluid in laminar flow. The streams of the first and second guide fluids have adjustable cross-sectional areas.
The body of the micro device includes a first pulse channel communicating with the channel. The first pulse channel has a first input portion with an output communicating with the channel and a second output portion with an input communicating with the channel. A pulse fluid flows between the output of the output portion of the first pulse channel and the input of the output portion first pulse channel.
The body may also include a second pulse channel communicating with the channel. The second pulse channel includes a first input portion having an output communicating with the channel and a second output portion having an input communicating with the channel. A second pulse fluid flows through the flow channel between the output of the output portion of the second pulse channel and the input of the output portion of the second pulse channel.
In accordance with a still further aspect of the present invention, a method is provided for examining and testing a biological object. The method includes the step of positioning a slice of the biological object in a channel of a micro device. A flow of stimulation fluid is directed over a user selected region of the slice. The flow of stimulation fluid may be constant or defined by a series of pulses of the stimulation fluid, such as a chemical agent.
The method may also include the additional step of supporting the slice on an array of electrodes. Electrical activity may be sensed at predetermined regions of the slice with the electrodes. In addition, a predetermined region of the slice may be stimulated with at least one of the electrodes.
The step of directing the flow of stimulation fluid may include the additional step of providing first and second guide fluids having variable cross sectional areas in the channel on opposite sides of the stimulation fluid. The first and second guide fluids and the stimulation fluid flow along corresponding axial flow paths in laminar flow. The cross sectional area of at least one guide fluid is varied so as to alter the axial flow path of the stimulation fluid.
The method of the present invention may include the additional step of stopping the flow of stimulation fluid. The step of stopping the stimulation fluid includes the additional step of providing first and second guide fluids having variable cross sectional areas in the channel on opposite sides of the stimulation fluid. The first and second guide fluids and the stimulation fluid flow along corresponding axial flow paths in laminar flow. Thereafter, the cross sectional area of at least one guide fluid is varied so as prevent the stimulation fluid for flowing therepast.